Variable geometry mirror having high-precision, high geometry controllability

ABSTRACT

A flexible thin film is supported by a frame member through two end portions opposing each other. A reflection surface is provided on the flexible thin film to reflect light. A first electrode is provided integrally with the flexible thin film. A second electrode is substantially fixed to the frame member so as to oppose the first electrode on an opposite side of the reflection surface. A third electrode is substantially fixed to the frame member so as to oppose the first electrode on the same side as the reflection surface. An optical opening for introducing light into the reflection surface is provided on the side of the reflection surface. At least one of the second and third electrodes is divided in the direction connecting the two end portions. The configuration of the reflection surface is controlled to a desired configuration by applying a desired voltage selectively to between the first electrode and the divided second or third electrode.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is based upon and claims the benefit of priority fromthe prior Japanese Patent Application No. 2001-282296, filed Sep. 17,2001, the entire contents of which are incorporated herein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a variable geometry cylinder mirror andmore particularly to a highly configurable, high precision cylindricallydeformable variable geometry mirror.

2. Description of the Related Art

In the field of high-precision micro optical systems such as an opticalpickup, a micro variable focus mirror capable of changing the curvatureof its reflecting face has been proposed so as to aim at simplificationof the structure for focusing, which conventionally uses anelectromagnetic actuator.

Further, in a small image pickup optical system, miniaturization islargely dependant on the size of the variable focus mirror.

Adoption of micro electromechanical system (MEMS) technology in avariable focus mirror enables low-cost, high-precision manufacturingthereof.

An example of the cylindrically deformable variable geometry cylindermirror of this technology is a monolithic reflecting mirror apparatusdisclosed in Jpn. Pat. Appln. KOKAI Publication No. 2-101402.

In this monolithic reflection mirror unit, as shown in FIG. 26, ametallic thin film 54, which serves as an electrode layer, is formed ona silicon semiconductor substrate 51, which acts as a fixed sideelectrode, through a silicon epitaxial layer 52 and a silicon oxide thinfilm 53. Window holes 56, 57 are formed in the silicon oxide thin film53 and the metallic thin film 54 with a central portion 55 left betweenthem.

Because the window holes 56, 57 communicate with each other through avacant portion 58 formed in the silicon epitaxial layer 52, the centralportion 55 is set up as a straddle-mounted type reflection mirrorportion.

The straddle-mounted type reflection mirror portion 55 opposes thesilicon semiconductor substrate 51 through the vacant portion 58. Byapplying a potential difference to 51 and 55, the reflection mirrorportion 55 is distorted, thereby functioning as a variable geometrycylinder mirror.

However, although the variable geometry cylinder mirror employing theconventional monolithic type reflection mirror unit can be soconstructed as a small, low-cost variable geometry cylinder mirror, theelectrostatic force applied to the reflection mirror portion cannot bechanged according to each position. Thus, this variable geometrycylinder mirror cannot be deformed to an asymmetrical shape.

Further, the variable geometry cylinder mirror using the conventionalmonolithic type reflection mirror unit can only be changed from a flatface to a concave face and it cannot be deformed to a convex shape.

Additionally, because the center of the reflection mirror portion alwaysdrops with deformation of the variable geometry cylinder mirror usingthe conventional monolithic type reflection mirror unit, there is aproblem that the curvature cannot be changed with the center portionfixed.

Further, the straddle mounted type structure is distorted by deformationof the reflection mirror portion. Thus, if a large distortion isdesired, a high voltage is needed in order to produce a largeelectrostatic force.

BRIEF SUMMARY OF THE INVENTION

The present invention has been achieved in view of the above-describedproblems and therefore, an object of the present invention is to providea small variable geometry cylinder mirror, the shape of which can befreely set and can also be asymmetrical.

Another object of the present invention is to provide a variablegeometry cylinder mirror, which can be deformed continuously from aconcave face to a convex face and further which can be deformed with thecenter or any point of the reflection mirror fixed.

Still another object of the present invention is to provide a variablegeometry cylinder mirror capable of obtaining large changes in curvaturewith a relatively low voltage.

In order achieve the above objects, according to a first aspect of thepresent invention, there is provided a variable geometry cylinder mirrorcomprising:

a frame member;

a flexible thin film in which two end portions opposing each other aresupported by the frame member;

a reflection surface which is provided on the flexible thin film andreflects light;

a first electrode provided integrally with the flexible thin film;

a second electrode substantially fixed to the frame member so as tooppose the first electrode on an opposite side of the reflectionsurface; and

a third electrode substantially fixed to the frame member so as tooppose the first electrode on the same side as the reflection surface,

wherein an optical opening to introduce light into the reflectionsurface is provided on the side of the reflection surface,

at least any one of the second and third electrodes is divided in thedirection connecting the two end portions, and

the configuration of the reflection surface is controlled to a desiredconfiguration by applying a desired voltage selectively to between thefirst electrode and the divided second or third electrode.

According to a second aspect of the present invention, there is provideda variable geometry cylinder mirror according to the first aspect,wherein the reflection surface of the flexible thin film is formed ofmetallic thin film and serves as the first electrode.

According to a second aspect of the present invention, there is provideda variable geometry cylinder mirror according to first aspect, whereinan openings are provided on both sides of the reflection surface in theflexible member across a straight line connecting the end portionssupported by the frame member.

According to a fourth aspect of the present invention, there is provideda variable geometry cylinder mirror according to the first aspect,wherein in a region between the end portion supported by the framemember and the reflection surface in the flexible thin film, stiffnessthereof in the direction in which the second or third electrode isdivided is decreased.

According to a fifth aspect of the present invention, there is provideda variable geometry cylinder mirror according to the fourth, wherein theregion in which the stiffness of the flexible thin film is dropped iswave-like.

According to a sixth aspect of the present invention, there is provideda variable geometry cylinder mirror according to the fifth aspect,wherein the flexible thin film is composed of overlaid layers ofmetallic thin film and silicon nitride or metallic thin film and siliconoxide.

According to a seventh aspect of the present invention, there isprovided a variable geometry cylinder mirror according to the fourthaspect, wherein as for the sectional area of the flexible thin film in adirection perpendicular to the direction in which the second or thirdelectrode is divided, that of the region in which the stiffness of theflexible thin film is dropped is smaller than that of a regioncorresponding to the reflection surface.

According to an eighth aspect of the present invention, there isprovided variable geometry cylinder mirror according to the fourthaspect, wherein an opening or a cutout is provided in the region inwhich the stiffness of the flexible thin film is dropped.

According to a ninth aspect of the present invention, there is provideda variable geometry cylinder mirror according to the first aspect,wherein the flexible thin film is composed of overlaid layers ofmetallic thin film and polymer material thin film.

According to a tenth aspect of the present invention, there is provideda variable geometry cylinder mirror according to the seventh aspect,wherein the flexible thin film is composed of overlaid layers ofmetallic thin film and polymer material thin film.

According to an eleventh of the present invention, there is provided avariable geometry cylinder mirror according to the eighth aspect,wherein the flexible thin film is composed of overlaid layers ofmetallic thin film and polymer material thin film.

According to a twelfth aspect of the present invention, there isprovided a variable geometry cylinder mirror according to the firstaspect, wherein the third electrode and a supporting member thereof areprovided outside the optical opening.

According to a thirteenth aspect of the present invention, there isprovided a variable geometry cylinder mirror according to the firstaspect, wherein the third electrode is disposed within the opticalopening while the third electrode disposed within the optical openingand the supporting member thereof have property allowing light to betransmitted through.

According to a fourteenth aspect of the present invention, there isprovided a variable geometry cylinder mirror comprising:

a frame member;

a flexible thin film in which two end portions opposing each other aresupported by the frame member;

a reflection surface which is provided on the flexible thin film andreflects light;

a first electrode provided integrally with the flexible thin film; and

a second electrode substantially fixed to the frame member so as tooppose the first electrode on an opposite side of the reflectionsurface, the second electrode being divided in the direction connectingthe two end portions,

wherein the configuration of the reflection is controlled to a desiredconfiguration by applying a desired voltage selectively to between thefirst electrode and the divided second or third electrode.

According to a fifteenth aspect of the present invention, there isprovided a variable geometry cylinder mirror according to the fourteenthaspect, wherein the reflection surface of the flexible thin film isformed of metallic thin film and serves as the first electrode.

According to a sixteenth aspect of the present invention, there isprovided a variable geometry cylinder mirror according to the fourteenthaspect, wherein an openings are provided on both sides of the reflectionsurface in the flexible member across a straight line connecting the endportions supported by the frame member.

According to a seventeenth aspect of the present invention, there isprovided a variable geometry cylinder mirror according to the fourteenthaspect, wherein in a region between the end portion supported by theframe member and the reflection surface in the flexible thin film,stiffness thereof in the direction in which the second electrode isdivided is decreased.

According to an eighteenth aspect of the present invention, there isprovided a variable geometry cylinder mirror according to theseventeenth aspect, wherein the region in which the stiffness of theflexible thin film is dropped is wave-like.

According to a nineteenth aspect of the present invention, there isprovided a variable geometry cylinder mirror according to the eighteenthaspect, wherein the flexible thin film is composed of overlaid layers ofmetallic thin film and silicon nitride or metallic thin film and siliconoxide.

According to a twentieth aspect of the present invention, there isprovided a variable geometry cylinder mirror according to theseventeenth aspect, wherein as for the sectional area of the flexiblethin film in a direction perpendicular to the direction in which thesecond electrode is divided, that of the region in which the stiffnessof the flexible thin film is dropped is smaller than that of a regioncorresponding to the reflection surface.

According to a twenty-first aspect of the present invention, there isprovided a variable geometry cylinder mirror according to theseventeenth aspect, wherein an opening or a cutout is provided in theregion in which the stiffness of the flexible thin film is dropped.

According to a twenty-second aspect of the present invention, there isprovided a variable geometry cylinder mirror according to the fourteenthaspect, wherein the flexible thin film is composed of overlaid layers ofmetallic thin film and polymer material thin film.

According to a twenty-third aspect of the present invention, there isprovided a variable geometry cylinder mirror according to the twentiethaspect, wherein the flexible thin film is composed of overlaid layers ofmetallic thin film and polymer material thin film.

According to a twenty-fourth aspect of the present invention, there isprovided a variable geometry cylinder mirror according to thetwenty-first aspect, wherein the flexible thin film is composed ofoverlaid layers of metallic thin film and polymer material thin film.

According to a twenty-fifth aspect of the present invention, there isprovided a variable geometry cylinder mirror according to the firstaspect, wherein the flexible thin film having the frame member, thereflection surface and the first electrode is manufactured by:

a diffused layer forming step of forming a diffused layer having apredetermined shape of a conductive type in a first main face of amono-crystal silicon substrate of another conductive type;

a thin film laminating step of laminating a thin film on the first mainface of the mono-crystal silicon substrate;

an etching step of, with a predetermined voltage applied to the diffusedlayer of the conductive type, carrying out electrochemical etching froma second main face in etching solution; and

a cutting and separating step of cutting and separating frame-likemono-crystal silicon which is part of the mono-crystal silicon substrateform portions corresponding to the flexible thin film and the framemember.

According to a twenty-sixth aspect of the present invention, there isprovided a variable geometry cylinder mirror according to the fourteenthaspect, wherein the flexible thin film having the frame member, thereflection surface and the first electrode is manufactured by:

a diffused layer forming step of forming a diffused layer having apredetermined shape of a conductive type in a first main face of amono-crystal silicon substrate of another conductive type;

a thin film laminating step of laminating a thin film on the first mainface of the mono-crystal silicon substrate;

an etching step of, with a predetermined voltage applied to the diffusedlayer of the conductive type, carrying out electrochemical etching froma second main face in etching solution; and

cutting and separating step of cutting and separating frame-likemono-crystal silicon which is part of the mono-crystal silicon substrateform portions corresponding to the flexible thin film and the framemember.

According to a twenty-seventh aspect of the present invention, there isprovided a variable geometry cylinder mirror according to the fifthaspect, wherein the flexible thin film having the frame member, thereflection surface and the first electrode is manufactured by:

a groove forming step of forming parallel grooves in a first main faceof a flat substrate;

a thin film forming step of forming a thin film on the first main faceof the substrate;

an etching step of etching until the thin film formed in the thin filmforming step is exposed from a second main face of the substrate; and

a cutting and separating step of cutting and separating a fame-likeportion which is part of the substrate from portions corresponding tothe flexible thin film and the frame member.

According to a twenty-eighth aspect of the present invention, there isprovided a variable geometry cylinder mirror according to the eighteenthaspect, wherein the flexible thin film having the frame member, thereflection surface and the first electrode is manufactured by:

a groove forming step of forming parallel grooves in a first main faceof a flat substrate;

a thin film forming step of forming a thin film on the first main faceof the substrate;

an etching step of etching until the thin film formed in the thin filmforming step is exposed from a second main face of the substrate; and

a cutting and separating step of cutting and separating a fame-likeportion which is part of the substrate from portions corresponding tothe flexible thin film and the frame member.

Additional objects and advantages of the invention will be set forth inthe description which follows, and in part will be obvious from thedescription, or may be learned by practice of the invention. The objectsand advantages of the invention may be realized and obtained by means ofthe instrumentalities and combinations particularly pointed outhereinafter.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING

The accompanying drawings, which are incorporated in and constitute apart of the specification, illustrate presently preferred embodiment ofthe invention, and together with the general description given above andthe detailed description of the preferred embodiment given below, serveto explain the principles of the invention.

FIGS. 1A and 1B are perspective views of an upper face and a lower faceshowing the entire structure of a variable geometry cylinder mirroraccording to a first embodiment of the present invention;

FIGS. 2A and 2B are perspective views of an upper face and a lower faceshowing a bottom substrate 101 of the variable geometry cylinder mirroraccording to the first embodiment of the present invention;

FIGS. 3A and 3B are perspective views of an upper face and a lower faceshowing an intermediate substrate 102 of the variable geometry cylindermirror according to the first embodiment of the present invention;

FIGS. 4A and 4B are perspective views of an upper face and a lower faceshowing a top substrate 103 of the variable geometry cylinder mirroraccording to the first embodiment of the present invention;

FIGS. 5A and 5B are enlarged views taken in the direction of an arrow Aand an arrow B shown in FIG. 1A;

FIG. 6 is a sectional view parallel to a slit-like opening portion 104in a region in which a lower electrode 109 and an upper electrode 117oppose each other for explaining the operation of the variable geometrycylinder mirror according to the first embodiment of the presentinvention;

FIG. 7 is a top view of the intermediate substrate 102 for explainingthe method of manufacturing the intermediate substrate of the variablegeometry cylinder mirror according to the first embodiment of thepresent invention;

FIGS. 8A and 8B are a sectional view taken along the line 8A—8A and asectional view taken along the line 8B—8B in FIG. 7;

FIGS. 9A and 9B are a sectional view taken along the line 9A—9A and asectional view taken along the line 9B—9B in FIG. 7;

FIGS. 10A and 10B are a sectional view taken along the line 10A—10A anda sectional view taken along the line 10B—10B in FIG. 7;

FIGS. 11A and 11B are perspective views of an upper face and a lowerface showing an intermediate substrate 201 of a variable geometrycylinder mirror according to a second embodiment of the presentinvention;

FIG. 12 is a sectional view taken along the line 12—12 in FIG. 11A;

FIG. 13 is a sectional view for explaining a method of manufacturing anintermediate substrate 201 of the variable geometry cylinder mirroraccording to the second embodiment of the present invention;

FIG. 14 is a sectional view for explaining the method of manufacturingthe intermediate substrate 201 of the variable geometry cylinder mirroraccording to the second embodiment of the present invention;

FIG. 15 is a sectional view for explaining the method of manufacturingthe intermediate substrate 201 of the variable geometry cylinder mirroraccording to the second embodiment of the present invention;

FIG. 16 is a sectional view for explaining the method of manufacturingthe intermediate substrate 201 of the variable geometry cylinder mirroraccording to the second embodiment of the present invention;

FIG. 17 is a sectional view for explaining the method of manufacturingthe intermediate substrate 201 of the variable geometry cylinder mirroraccording to the second embodiment of the present invention;

FIG. 18 is a sectional view for explaining the method of manufacturingthe intermediate substrate 201 of the variable geometry cylinder mirroraccording to the second embodiment of the present invention;

FIG. 19 is a sectional view for explaining the method of manufacturingthe intermediate substrate 201 of the variable geometry cylinder mirroraccording to the second embodiment of the present invention;

FIGS. 20A and 20B are perspective views of an upper face and a lowerface showing an intermediate substrate 400 of a variable geometrycylinder mirror according to a third embodiment of the presentinvention;

FIGS. 21A and 21B are perspective views of an upper face and a lowerface showing a top substrate 501 of a variable geometry cylinder mirroraccording to a fourth embodiment of the present invention;

FIGS. 22A and 22B are perspective views of an upper face and a lowerface showing a bottom substrate 108 of a variable geometry cylindermirror according to a fifth embodiment of the present invention;

FIGS. 23A and 22B are perspective views of an upper face and a lowerface showing a top substrate 608 of the variable geometry cylindermirror according to a fifth embodiment of the present invention;

FIGS. 24A and 24B are perspective views of an upper face and a lowerface showing a bottom substrate 801 of a variable geometry cylindermirror according to a sixth embodiment of the present invention;

FIGS. 25A and 25B are enlarged views taken in the direction of an arrowA and an arrow B in FIG. 24A; and

FIG. 26 is a perspective view showing the main structure of a monolithictype reflection mirror unit disclosed in Jpn. Pat. Appln. KOKAIPublication No. 2-101402 as an example of a conventional variablegeometry cylinder mirror which is deformed cylindrically.

DETAILED DESCRIPTION OF THE INVENTION

Reference will now be made in detail to the preferred embodiments of theinvention as illustrated in the accompanying drawings, in which likereference numerals designate like or corresponding parts.

Hereinafter, the preferred embodiments of the present invention will bedescribed with reference to the accompanying drawings.

(First Embodiment)

A variable geometry cylinder mirror according to a first embodiment ofthe present invention will be described with reference to FIGS. 1A, 1Bto 10A, 10B.

FIGS. 1A and 1B are perspective views of an upper face and a lower faceshowing the entire structure of the variable geometry cylinder mirroraccording to the first embodiment of the present invention.

The variable geometry cylinder mirror is constituted of three layers: abottom substrate 101, an intermediate substrate 102 and an top substrate103, disposed with a constant space specified by each spacer.

The top substrate 103 has a slit-like opening portion 104 formedtherein, for introducing light.

As evident from the same Figure, the bottom substrate 101 and the topsubstrate 103 are projected with respect to the intermediate substrate102 in opposite directions.

A lower electrode pad 105 is formed on a projected portion of the bottomsubstrate 101.

An upper electrode pad 106 and an intermediate electrode pad 107 areformed on a projected portion of the top substrate 103.

FIGS. 2A and 2B are perspective views of an upper face and a lower faceshowing the bottom substrate 101.

The bottom substrate 101 is made of mono-crystal silicon substrate 108having a thickness of 300 μm, and has a plurality of lower electrodes109 disposed symmetrically across a region opposing the slit-likeopening portion 104 formed in the top substrate 103. The lower electrodepads 105 and connection spacers 110 have a height of 30 μm relative tothe top substrate 103.

The silicon substrate 108 has a wiring layer which connects therespective lower electrodes 109 and lower electrode pads 105 through aninterlayer insulating film and contact holes (not shown).

Such multi-layer electrodes and wiring can be formed easily on thesilicon substrate 108 using ordinary integrated circuit manufacturingtechnology.

FIGS. 3A and 3B are perspective views of upper face and lower faceshowing the intermediate substrate 102.

This intermediate substrate 102 has a flexible thin film 112 formed on amono-crystal silicon substrate 111 having the thickness of 20 μm, theflexible thin film 112 being comprised of polyamide film 1 μm thick andAu/Cr overlaid film 50 μm thick.

The flexible thin film 112 is exposed to an opposite side of themono-crystal substrate 111 as Au, acting as reflection faces.

A rectangular opening portion 113 and a cutout portion 114 are formed inthe mono-crystal silicon substrate 111, through which the flexible thinfilm 112 is exposed, the mono-crystal silicon substrate 111 beingdeformable with a slight stress.

Cutouts 115 are formed in the flexible thin film 112 along two side endsparallel to the slit-like opening portion 104 in the top substrate 103,in the opening portion 113. The flexible thin film 112 is like a beltsupported by two sides perpendicular to the slit-like opening portion104 in the top substrate 103.

FIGS. 4A and 4B are perspective views of an upper face and a lower faceshowing the top substrate 103.

This top substrate 103 is made of a mono-crystal silicon substrate 116having a thickness of 300 μm, a plurality of upper electrodes 117disposed in the form of a belt symmetrically with respect to theslit-like opening portion 104, the upper electrode pad 106, theintermediate electrode pad 107, an intermediate electrode lead-outelectrode 118, a connecting spacer 120 having a height of 30 μm to thebottom substrate 101 and a connecting spacer 121 having a height of 30μm to the intermediate substrate 102.

The silicon substrate 116 contains wiring layer (not shown) whichconnects the respective upper electrodes 117, intermediate electrodelead-out electrode 118, upper electrode pad 106 and intermediateelectrode pad 107 through an interlayer insulating film and contactholes (not shown).

Such multi-layer electrodes and wiring can be formed easily on thesilicon substrate 116 using ordinary integrated circuit manufacturingtechnology.

The slit-like opening portion 104 can be formed easily by usingtechnology applied to ordinary MEMS device such as anisotropic etchingfor silicon using strong alkali solution.

Next, connection of the bottom substrate 101, intermediate substrate 102and top substrate 103 will be described with reference to FIGS. 5A and5B.

FIGS. 5A and 5B are enlarged views taken in the direction of arrows Aand B in FIG. 1A.

That is, in these diagrams, its vertical directions are enlarged tofacilitate understanding.

The connecting spacer 110 of the bottom substrate 101 is connected withthe connecting spacer 120 of the top substrate 103.

Because the height of each of the connecting spacer 110 and connectingspacer 120 is 30 μm, the bottom substrate 101 and the top substrate 103oppose each other with a gap of 60 μm.

The intermediate substrate 102 is connected with the top substrate 103through the connecting spacer 121.

The height of the connecting spacer 121 is 30 μm like the connectingspacer 110 and connecting spacer 120.

Consequently, the flexible thin film 112 on the intermediate substrate102 is located substantially in the middle of the gap between the bottomsubstrate 101 and the top substrate 103.

Various kinds of materials can be considered as raw material for therespective connecting spacers 110, 120, 121. If easiness ofmanufacturing is taken into account, particularly, material which can befused with heat and patterned by photolithography method is preferred.

An Au bump 119 having the height of 40 μm formed on the intermediateelectrode lead-out electrode 118 on the top substrate 103 opposessubstantially the center of the rectangular opening portion 113 andcutout 114 formed in the mono-crystal silicon substrate 111 of theintermediate substrate 102. Because the height of this Au bump 119 isslight larger than that of the connecting spacer 121 of the intermediatesubstrate 102, the flexible thin film 112 is pushed up by this portion.As a result, the Au bump 119 is electrically connected to theintermediate electrode pad 107 through the intermediate electrodelead-out electrode 118 on the top substrate 103 because metallic film isexposed on the surface of the flexible thin film 112.

At this time, the flexible thin film 112 is deformed in the region ofthe cutout 114. However, the deformation of the flexible thin film 112in the region of the cutout 114 never affects the flexible thin film 112in the region of the opening portion 113 because the flexible thin film112 is separated by the silicon thin plate 111 having a sufficientlyhigher stiffness than the flexible thin film 112.

Because the lower electrode pad 105 and the upper electrode pad 106correspond to the lower electrode 109 and the upper electrode 106,respectively while the flexible thin film 112 is connected to theintermediate electrode pad 107, if an external lead wire is connected tothe electrode pads 105, 106, 107 so as to connect them to independentpower supplies, independent voltage can be applied to each of theflexible thin film 112, the lower electrode 109 and the upper electrode117.

Next, the operation of the variable geometry cylinder mirror of thisembodiment will be described with reference to FIG. 6.

FIG. 6 shows a sectional view parallel to the slit-like opening portion104 in the region in which the lower electrode 109 and the upperelectrode 117 oppose each other.

If the flexible thin film 112, all the lower electrodes 109 and all theupper electrodes 117 are grounded, the flexible thin film 112 turns intoa flat shape as indicated with dotted line in the same Figure. If a highvoltage is applied to the upper electrodes 117-1, 117-2, 117-5, 117-6and the lower electrodes 109-3, 109-4 while the flexible thin film 112,the upper electrodes 117-3, 117-4 and the lower electrodes 109-1, 109-2,109-5, 109-6 are grounded, the flexible thin film turns to an indicatedwave-like shape.

If the voltage applied to the upper electrodes 117-1, 117-2 is slightlyhigher than that applied to the upper electrodes 117-5, 117-6, anasymmetrical deformation shape with respect to the center can beobtained as indicated in the same Figure.

By adjusting the voltage applied to the lower electrodes 109 and theupper electrode 117, the flexible thin film 112 can be deformed into anyshape.

According to this embodiment, although no electrode for activatingelectrostatic force is formed just below the region of the top substratein which the slit-like opening portion 104 is formed, its influence canbe reduced to a level which can be neglected by increasing the width ofthe top electrode 117 and the bottom electrode 109 so as to be muchlarger than the width of this region.

Additionally, according to this embodiment, power consumption can bekept very low by using an electrostatic force for driving and becausethe structure is simple, it can be miniaturized.

Further, this embodiment enables deformation to both a concave shape anda convex shape and driving force can be controlled independently foreach region opposing the electrode. Therefore, for example, the flexiblethin film can be changed from the concave face to the convex facewithout deflecting the center of the mirror or any one point verticallyby controlling the distribution of the driving force appropriately.

This feature cannot be acquired from an air pressure type variablegeometry mirror.

Further, because light enters directly into the flexible thin film 112which acts as a reflection surface through the slit-like opening portion104, no glass face or the like exists between incident light and thereflection surface. Thus, there is no loss of light beam, change in beampath length or deterioration of focusing performance.

Although according to this embodiment, the upper electrode 117 and thelower electrode 109 are divided substantially into six equal sections,needless to say, the number of electrodes may be changed or theelectrodes may be divided unequally depending on a desired configurationor accuracy.

Next, the method of manufacturing the intermediate substrate of thevariable geometry cylinder mirror of this embodiment will be describedwith reference to FIGS. 7 to 10B.

FIG. 7 shows a top view of the intermediate substrate 102. Sections8A—8A, 9A—9A and 10A—10A in FIG. 7 will be described with reference toFIGS. 8A, 9A and 10A.

Further, the sections 8B—8B, 9B—9B and 10B—10B in FIG. 7 will bedescribed with reference to FIGS. 8B, 9B and 10B.

As shown in FIGS. 8A and 8B, an N-type impurity diffused layer 123 isformed in a P-type low density semiconductor substrate (mono-crystalsemiconductor substrate) 122.

A silicon nitride film 124 is formed on both faces of the P-type lowdensity semiconductor substrate (mono-crystal semiconductor substrate)122.

An opening pattern larger than the intermediate substrate 102 is formedon the rear side of the silicon nitride film 124.

If viewed from above, the region in which the N type impurity diffusedlayer 123 is formed is substantially equal to the region of theintermediate substrate 102 in which the mono-crystal silicon substrate111 is formed.

Further, it is preferable if the silicon nitride film 124 imparts asmall stress on the silicon substrate 122, by appropriately controllingthe composition of that film.

Next, a polyimide film 125 having a thickness of 1 μm and a metallicfilm 126 having a thickness of 0.1 μm are formed successively on thesilicon nitride film 124.

Then, the metallic film 126 is patterned.

The metallic film 126 and the polyimide film 125 are removed bypatterning in the region of the cutout 115 shown in FIG. 7.

Preferably, a very thin chrome thin film is formed between the polyimidefilm 125 and the metallic thin film 126, thus adhesion of the metallicfilm 126 is improved.

Prior to formation of the metallic film 126, a contact hole 127 isformed in the polyimide film 125 and the silicon nitride film 124 on thefront surface, so that the metallic film 126 is electrically conductivewith the N-type impurity diffused layer 123.

Next, as shown in FIGS. 9A and 9B, with the front surface protected bymechanical sealing or the like, electrochemical etching is carried outwith a strong alkali solution by applying a positive voltage to themetallic thin film 126.

Because the metallic film 126 is conductive with the N-type impuritydiffused layer 123, etching is progressed in the region in which thesilicon nitride film 124 on the front surface is removed by patterninguntil the silicon nitride film 124 on the front surface is exposed withthe region of the N-type impurity diffused layer 123 left.

Next, as shown in FIGS. 10A and 10B, the silicon nitride film on theexposed suction face on the rear side and front side is removed byreactive ion etching from the rear side.

By cutting out the polyimide film 125 along the outer shape of the leftN-type impurity diffused layer 123 according to excimer laser aberrationor the like, the intermediate substrate 102 is obtained.

Although this embodiment indicates one manufacturing method of theintermediate substrate, it is needless to say that actually, a pluralityof the intermediate substrates are obtained from one silicon wafer.

According to this method of manufacturing the intermediate substrate, asit can be formed in a completely monolithic way according to ordinarysemiconductor manufacturing technology and MEMS technology, excellentproductivity and safety are ensured.

Particularly, the manufacturing method of this embodiment in which theflexible thin film is formed on a thick solid substrate while thesubstrate is turned into thin film by electrochemical etching ispreferable for an application requiring a high accuracy reflectionsurface in that there is no distortion accompanying a machining processfor a frame member.

(Second Embodiment)

A second embodiment of the present invention will be described withreference to FIGS. 11A to 19.

This embodiment is different from the first embodiment only in theintermediate substrate.

FIGS. 11A and 11B are perspective views of an upper face and a lowerface showing the structure of an intermediate substrate 201 of avariable geometry cylinder mirror according to the second embodiment ofthe present invention.

Basically, the intermediate substrate 201 of this embodiment has thesame configuration as the intermediate substrate 102 of the firstembodiment shown in FIGS. 3A and 3B. A flexible thin film 203 comprisingsilicon nitride film 400 nm thick and metallic thin film 50 nm thick isformed on the top face of a thin mono-crystal silicon substrate 202having the thickness of 20 μm which serves as a frame member.

Here it is assumed that the metallic thin film is exposed to the topface.

In the same manner as in the first embodiment, a rectangular openingportion 204 and a cutout 205 are formed in the mono-crystal siliconsubstrate 202 and a belt-like flexible thin film 203 is exposed in thisportion and deformable with a slight stress.

Like the first embodiment, in the opening portion 204, cutouts 206 areformed in the flexible thin film 203 on its ends along two sidesparallel to the slit-like opening 104 in the top substrate 103 and theflexible thin film 203 is shaped in the form of a belt supported by twosides perpendicular to the slit-like opening 104 in the top substrate103.

A wave-like portion 207 of the flexible thin film 203 is formed near thetwo sides supporting the flexible thin film 203.

Next, FIG. 12 shows a section taken along the line 12—12 in FIG. 11A.

The flexible thin film 203 constructs the wavelike portion 207 in thevicinity of its sides supported by the thin mono-crystal siliconsubstrate 202 which acts as a frame member.

The variable geometry cylinder mirror of this embodiment is driven inthe same manner as the variable geometry cylinder mirror of the firstembodiment shown in FIG. 6. Because both the ends of the flexible thinfilm 203 are constructed in the form of a wave, it is expanded orcontracted easily through this portion. Thus, if material having a largelongitudinal elastic modulus like silicon nitride film is utilized asthe flexible thin film 203 in the variable geometry cylinder mirror ofthe first embodiment, a relatively large deflection can be secured evenwhen a high voltage is not applied to the same upper electrode 117 orlower electrode 109 as in the variable geometry cylinder mirror of thefirst embodiment.

That is, the mechanical properties of the silicon nitride film onlyslightly change over time, and its stiffness remains substantially high.This embodiment is preferable for long term use in high temperature andhumidity environments.

Preferably, the wave-like portion 207 is located near the end portion,away from direct light.

Although in this embodiment, the wave-like portion 207 is provided onboth end portions, it is needless to say that it could be provided onone side only.

Next, a method of manufacturing the intermediate substrate 201 of thevariable geometry cylinder mirror according to the second embodiment ofthe present invention will be described with reference to FIGS. 13 to16.

A silicon nitride film is formed on both faces of an overlay type SOIsubstrate in which as shown in FIG. 13, a mono-crystal silicon activelayer 303 having a thickness of 20 μm is bonded to a mono-crystalsilicon substrate 301 having a face bearing of <100>, 500 μm thickthrough a silicon oxide film 302.

Then, upper and rear face silicon nitride films 304 and 305 are formedby patterning.

Next, as shown in FIG. 14, the mono-crystal silicon active layer 303 ispatterned by reactive ion etching with the upper face silicon nitridepattern 304 as a mask. Consequently, a thin silicon region correspondingto the frame member 202 is formed as shown in FIG. 12.

Next, as shown in FIG. 15, an opening portion 306 is formed in theexposed silicon oxide film 302 with ordinary photolithographytechnology.

Next, as shown in FIG. 16, anisotropic etching is carried out in theopening portion 306 up to 2 μm with tetramethyl ammonium hydroxide(YMAH) with the rear face protected and the silicon oxide film 302 as amask, so that a depression 307 is formed.

Next, as shown in FIG. 17, the exposed silicon oxide film 302 is removedby hydrogen fluoride acid.

Next, as shown in FIG. 18, a silicon nitride film 308 is formed on thetop face according to the chemical vapor deposition (CVD) method.

At this time, at a portion in which the dent portion 307 is formed, thesilicon nitride film 308 is turned to a wave-like portion 309.

Next, as shown in FIG. 19, with the front face protected and the siliconnitride film pattern 305 as a mask, the silicon substrate 301 is etcheduntil the silicon nitride film 308 is exposed.

After that, the thin mono-crystal silicon substrate 202 is cut out alongits outer periphery as a frame member shown in FIG. 12 and theintermediate substrate 201 is formed by depositing Au/Cr thin film on anopposite side to the thin mono-crystal silicon substrate 202 of thesilicon nitride film 308.

According to the method of manufacturing the intermediate substrate ofthis embodiment, the stabilized fine wave-like structure can be achievedby using the ordinary MEMS technology, because steps of forming a groovein the mono-crystal silicon substrate 301 according to thephotolithography technology, forming the silicon nitride film equallyalong this configuration and then removing the substrate after that, areadopted.

Although the active layer of the SOI substrate is used as the framemember of the intermediate substrate, a thin mono-crystal siliconforming step may be adopted by using electrochemical etching, in thesame manner as in the first embodiment.

According to the method of manufacturing the intermediate substrate ofthis embodiment, the substrate cost is higher than the method of usingelectrochemical etching, and the flatness achieved on the substrate isslightly worse. However, because the step of forming the diffused layercan be omitted, the device can be produced in less time.

(Third Embodiment)

A third embodiment will be described with reference to FIGS. 20A and20B. This embodiment is different from the first embodiment only in thestructure of the intermediate substrate.

FIGS. 20A and 20B are perspective views of an upper face and a lowerface showing an intermediate substrate 400 of a variable geometrycylinder mirror according to the third embodiment of the presentinvention.

Although basically this intermediate substrate 400 has the flexible thinfilm 112 composed of mainly polyimide film like the first embodiment, aplurality of circular opening portions 401 are formed in the vicinity ofsides supported by the thin mono-crystal silicon 111.

This circular opening portion 401 may be formed by using aphotolithography method at the same time when the cutout 115 is formed.

This method does not increase the quantity of steps, as compared to thefirst embodiment.

According to this embodiment, stiffness in the vicinity of the sidesupported side of the flexible thin film 112 is reduced by the circularopening portion 401, so that expansion/contraction are enabled by asmaller electrostatic attracting force. As a result, the driving voltagecan be reduced as compared to the first embodiment.

According to this embodiment, the plurality of circular opening portions401 are provided to achieve low stiffness in part of the flexible thinfilm 112. Needless to say, the shape of this opening portion 401 may beformed in various ways such as rectangular shape, slit, etc.

The same effect can be obtained by providing a U-like cutout orpartially thinning, as well as by using a complete opening shape.

That is, by setting smaller the sectional area used for achieving lowstiffness in the flexible thin film than the other portions, thestiffness may be adjusted just at a desired portion.

(Fourth Embodiment)

A fourth embodiment will be described with reference to FIGS. 21A and21B.

This embodiment is different from the first embodiment only in thestructure of the top substrate.

FIGS. 21A and 21B are perspective views of an upper face and a lowerface showing the structure of an upper substrate 501 according to thefourth embodiment of the present invention.

The structure of this top substrate 501 is similar to that of the topsubstrate 103 of the first embodiment, but different in that a quartzsubstrate 501 is used as the substrate and the slit-like opening portion104 is omitted.

Because no electrode is formed in a region irradiated with incidentlight if the substrate is constructed of a transparent quartz, theincident light can reach the intermediate substrate having a reflectionsurface, without providing with any opening.

A portion indicated by dotted line in FIGS. 21A and 21B is a regionthrough which light enters the flexible thin film.

That is, according to this embodiment, by forming a substrate located inthe region irradiated with the incident light of transparent quartzwithout providing the top substrate with any opening, an optical openingcan be secured.

Although in this embodiment, focusing performance is affected by aninfluence of distortion of the quartz substrate 501, particularly, thisembodiment does not suit to high precision applications. However it ispreferable for an application demanding for reduction of cost becausethe manufacturing method can be simplified.

In the meantime, needless to say, any other material may be used insteadof quartz as long as it allows light through it.

(Fifth Embodiment)

A fifth embodiment will be described with reference to FIGS. 22A, 22B,23A and 23B.

This embodiment is different from the first embodiment in the structuresof the bottom substrate and the top substrate.

FIGS. 22A and 22B are perspective views of an upper face and a lowerface showing the structure of a bottom substrate 508 of a variablegeometry cylinder mirror according to the fifth embodiment of thepresent invention.

According to the first embodiment shown in FIGS. 2A and 2B, no electrodeis formed just below a light receiving portion while the lowerelectrodes 109 are disposed symmetrically on both sides of this region.However, according to this embodiment, top electrodes are formed suchthat the electrodes on both sides are combined.

FIGS. 23A and 23B are perspective views of an upper face and a lowerface showing the structure of a top substrate 608 of the variablegeometry cylinder mirror according to a fifth embodiment of the presentinvention.

As for the top substrate 608, as shown in FIGS. 23A and 23B, thatsubstrate is the same transparent quartz substrate 608 same as in thefourth embodiment, the electrode is composed of a transparent ITO andthe upper electrodes 602 are disposed on the light receiving portionalso.

A portion indicated with dotted line in FIGS. 23A and 23B is a regionthrough which light enters the flexible thin film.

In the same manner as in the fourth embodiment, this embodiment adopts alight transparent material for a substrate and electrodes which lightenters and secures an optical opening in order to make light enter intothe flexible thin film.

According to this embodiment, a plurality of electrodes are disposed onboth faces opposing the flexible thin film on the intermediatesubstrate. Because the top substrate and the upper electrodes are formedof a transparent material, the electrodes can be disposed just over alight receiving portion of the top substrate.

According to this embodiment, beam path length changes depending on theposition of the incident light and focusing performance deterioratebecause the quartz substrate 608 and the upper electrodes 602 existbetween incident light and a light receiving position. However, this ispreferable for a case where the width of the incident light is large orpositioning of a variable geometry mirror relative to incident light isdifficult.

The problem of the above-described deterioration in focusing performancecan be avoided to some extent, if, after the upper electrodes 602 areformed, the top face of the quartz substrate 608 is coated with adielectric film having substantially the same refractivity as the upperelectrodes 602, and this film is flattened.

Although the upper and lower electrodes 602, 601 are symmetrical to theflexible thin film on the intermediate substrate, they may beasymmetrical in the same way, as described in the first embodiment.

For example, if the upper electrode 601 is composed of a singleelectrode opposing the entire range of the flexible thin film on theintermediate substrate while the electrostatic attracting force appliedto the divided lower electrodes is differed according on each position,the flexible thin film can be deformed unevenly.

(Sixth Embodiment)

A sixth embodiment of the present invention will be described withreference to FIGS. 24A, 24B, 25A and 25B.

This embodiment adopts a two-layer structure by omitting the topsubstrate 103 of the first embodiment.

Its basic operating principle is the same as the above-describedembodiment. Although it is incapable of controlling high-precisionunevenness in the configuration, this embodiment is more advantageoussince the number of electrodes can be reduced.

FIGS. 24A and 24B are perspective views of an upper face and a lowerface showing the structure of a lower substrate 801 of a variablegeometry cylinder mirror according to the sixth embodiment of thepresent invention.

FIGS. 25A and 25B are enlarged views taken in the direction of arrows Aand B in FIG. 24A, indicating the assembly diagram of this embodiment.

These figures are represented in enlargement in the vertical directionto facilitate understanding.

Differences in terms of structure between this embodiment employing thetwo-layer structure and the three-layer structure of the firstembodiment are as follows.

(1) Forming the intermediate substrate electrode lead-out pad on the topsubstrate and the Au bump formed thereon on the lower substrate.

(2) Connecting the intermediate substrate to the spacer member on thelower substrate.

Because the polyimide film side is joined to the spacer on the lowersubstrate, the installation direction is reverse to the three-layerstructure.

(3) Thus, the Au thin film needs to be deposited on the side of the thinmono-crystal silicon substrate of the intermediate substrate as areflection surface.

Thus, as described above, the present invention can provide a smallvariable geometry cylinder mirror which can be changed to a freeconfiguration including an asymmetrical one.

Further, the present invention is capable of providing a variablegeometry cylinder mirror which can be changed continuously from theconcave face to the convex face and further which can be deformed withthe center or any point in its reflection mirror portion fixed.

Further, the present invention can provide a variable geometry cylindermirror which can obtain large changes in curvature with a relatively lowvoltage.

Additional advantages and modifications will readily occur to thoseskilled in the art. Therefore, the invention in its broader aspects isnot limited to the specific details and representative embodiments shownand described herein. Accordingly, various modifications may be madewithout departing from the spirit or scope of the general inventiveconcept as defined by the appended claims and their equivalents.

What is claimed is:
 1. A variable geometry cylinder mirror comprising: aframe member; a flexible thin film in which two end portions opposingeach other are supported by said frame member; a reflection surfacewhich is provided on said flexible thin film and reflects light; a firstelectrode provided integrally with said flexible thin film; a secondelectrode substantially fixed to said frame member so as to oppose saidfirst electrode on an opposite side of said reflection surface; and athird electrode substantially fixed to said frame member so as to opposesaid first electrode on the same side as said reflection surface,wherein an optical opening to introduce light into said reflectionsurface is provided on the side of said reflection surface, at least anyone of said second and third electrodes is divided in the directionconnecting said two end portions, and the configuration of saidreflection surface is controlled to a desired configuration by applyinga desired voltage selectively to between said first electrode and saiddivided second or third electrode.
 2. The variable geometry cylindermirror according to claim 1, wherein the reflection surface of saidflexible thin film is formed of metallic thin film and serves as saidfirst electrode.
 3. The variable geometry cylinder mirror according toclaim 1, wherein an openings are provided on both sides of saidreflection surface in said flexible member across a straight lineconnecting the end portions supported by said frame member.
 4. Thevariable geometry cylinder mirror according to claim 1, wherein in aregion between the end portion supported by said frame member and saidreflection surface in said flexible thin film, stiffness thereof in thedirection in which said second or third electrode is divided is reduced.5. The variable geometry cylinder mirror according to claim 4, whereinthe region in which the stiffness of said flexible thin film is reducedis wave-like.
 6. The variable geometry cylinder mirror according toclaim 5, wherein said flexible thin film is composed of overlaid layersof metallic thin film and silicon nitride or metallic thin film andsilicon oxide.
 7. The variable geometry cylinder mirror according toclaim 4, wherein as for the sectional area of said flexible thin film ina direction perpendicular to the direction in which said second or thirdelectrode is divided, that of the region in which the stiffness of saidflexible thin film is reduced is smaller than that of a regioncorresponding to said reflection surface.
 8. The variable geometrycylinder mirror according to claim 4, wherein an opening or a cutout isprovided in the region in which the stiffness of said flexible thin filmis reduced.
 9. The variable geometry cylinder mirror according to claim1, wherein said flexible thin film is composed of overlaid layers ofmetallic thin film and polymer material thin film.
 10. The variablegeometry cylinder mirror according to claim 7, wherein said flexiblethin film is composed of overlaid layers of metallic thin film andpolymer material thin film.
 11. The variable geometry cylinder mirroraccording to claim 8, wherein said flexible thin film is composed ofoverlaid layers of metallic thin film and polymer material thin film.12. The variable geometry cylinder mirror according to claim 1, whereinsaid third electrode and a supporting member thereof are providedoutside said optical opening.
 13. The variable geometry cylinder mirroraccording to claim 1, wherein said third electrode is disposed withinsaid optical opening while said third electrode disposed within saidoptical opening and the supporting member thereof have property allowinglight to be transmitted through.